This invention relates to coated glass used in residential, architectural and vehicle windows and miscellaneous applications where both solar control and low emissivity properties are desired. The coatings for solar control and low emissivity contain tin oxide having various dopants. The invention avoids the need for an anti-iridescence underlayer. The glass articles may be of any shape but are typically flat or curved. The glass composition can very widely but is typically soda lime glass produced by the float process. It may be annealed, heat strengthened or tempered.
Solar-control is a term describing the property of regulating the amount of solar heat energy which is allowed to pass through a glass article into an enclosed space such as a building or an automobile interior. Low emissivity is a term describing the property of an article""s surface wherein the absorption and emission of mid-range infrared radiation is suppressed, making the surface a mid-range infrared reflector and thereby reducing heat flux through the article by attenuating the radiative component of heat transfer to and from the low emissivity surface (sometimes referred to as Low E). By suppressing solar heat gain, building and automobile interiors are kept cooler, allowing a reduction in air conditioning requirements and costs. Efficient low emissivity coatings improve comfort during both summer and winter by increasing the thermal insulating performance of a window.
Important to commercially acceptable coated glass articles which possess both solar-control and low emissivity properties are, of course, economic processes for producing the articles and durability and maintenance of associated properties such as light transmission, visibility, color, clarity and reflection.
As explained below, various technologies have been employed to meet the requirement for solar-control and low emissivity glass, however, no one system has successfully met all of the performance requirements in an economic manner.
Many coatings and coating systems cause iridescent colors to develop in the coated article. This may be caused by the chemical composition of the coating, the thickness of an individual layer or layers, or an interaction of the substrate and coatings to incident light. Such iridescence can, in some cases, be minimized or eliminated by placing an anti-iridescence layer between the glass substrate and the first coating. The use of an interference layer between the glass and a subsequent functional layer or layers to suppress iridescence or color reflection was first demonstrated by Roy G. Gordon, and was the subject of U.S. Pat. No. 4,187,336, issued Feb. 5, 1980. The Gordon technology has been the state of the art for coated solar control glass as evidenced by recently issued U.S. Pat. No. 5,780,149 (McCurdy et al, Jul. 14, 1998) which applied two layers to obtain solar control on top of a Gordon type interference layer. The interference layer frequently contains silicon dioxide. Surprisingly, the present invention represents a dramatic breakthrough and eliminates the need for a Gordon type underlayer to control reflected color.
U.S. Pat. No. 3,149,989 discloses compositions of coatings useful in producing radiation reflecting (solar-control) glass. At least two coatings are used with the first coating, adhered to the glass substrate, being comprised of tin oxide doped with a relatively high level of antimony. The second coating is also comprised of tin oxide and is doped with a relatively low level of antimony. The two films may be superimposed, one on another, or may be applied to opposite sides of the glass substrate. In either case, these solar-control coatings do not contribute significant low emissivity properties to the glass article.
U.S. Pat. No. 4,287,009 teaches a heat absorbing glass designed to convert incident sun rays into heat energy that is transferred to a working fluid for heat transfer. Accordingly, the coated glass absorbs at least 85% of the solar wavelength range rays and has a relatively low emissivity characteristic of less than 0.2. The coatings are positioned on the outside of the glass (i.e. the side facing the sun) and the fluid for heat transfer contacts the inside surface of the glass. The coatings comprise a first coating of metal oxides deposited on the smooth glass layer which oxides are selected from tin, antimony, indium, and iron and a second coating of metal oxides deposited on the first coating selected from the same group of metals. The films as designed will have very low visible transmissions and no teaching on the control of reflected color is given.
U.S. Pat. No. 4,601,917 teaches liquid coating compositions for producing high-quality, high-performance, fluorine-doped tin oxide coatings by chemical vapor deposition. One of the uses of such coatings is in the production of energy-efficient windows, also known in the trade as low-E or low-E windows. Methods of producing the coated glass are also described. This patent does not teach how to produce coated glass articles which possess both solar-control and low emissivity properties.
U.S. Pat. No. 4,504,109, assigned to Kabushiki Kaisha Toyota Chou, describes glass coated with infrared shielding multilayers comprising a visible light transparent substrate and an overlying component lamination consisting of xe2x80x9cat least one infrared shield layer and at least one interferential reflection layer alternatively lying on each other . . . xe2x80x9d Indium oxide doped with Sn is used in the examples as the infrared shield layer and TiO2 was used as the interferential shield layer. In order to reduce iridescence the infrared shield layer and the interferential reflection layer thickness must have a value of one quarter lambda (lambda/4) with a permissible deviation of from 75% to 130% of lambda/4. Although other formulations are disclosed for the infrared shield layer and the interferential reflection layer such as SnO2 with or without dopants, (see column 6 lines 12 to 27), however, the specific combination of doped SnO2 layers of the present invention that accomplishes solar control, low emissivity and anti-iridescence without requiring a lambda/4 thickness limitation is neither disclosed nor exemplified to suppress iridescence or color reflection.
U.S. Pat. No. 4,583,815, also assigned to Kabushiki Kaisha Toyota Chou describes a heat wave shield laminate consisting of two indium tin oxide overlayers containing different amounts of tin. Antireflection layers, above or below the indium tin oxide layers are also described. Other formulations are disclosed for the infrared shield layer and the interferential reflection layer such as SnO2 with a dopant that becomes a positive ion with a valence of +5 such as Sb, P, As, Nb, Ta, W, or Mo or an element such as F which readily becomes a negative ion with a valence of xe2x88x921, (see column 22 lines 17 to 23). However, the specific combination of doped SnO2 layers of the present invention that accomplishes solar shielding, low emissivity and anti-iridescence is neither disclosed nor exemplified. There is no claim to tin oxide layers nor any teaching in the specification to describe the composition of such layers, e.g. the ratio of dopant to tin oxide. It should also be noted that the teaching leads to the use of the same dopant in both layers (indium tin oxide) whereas in the instant patent application, one layer must contain a different dopant than the other layer.
U.S. Pat. No. 4,828,880, assigned to Pilkington PLC, describes barrier layers which act to inhibit migration of alkali metal ions from a glass surface and/or act as color suppressing underlayers for overlying infrared reflecting or electrically conducting layers. Some of these color suppressing layers are used in solar-control or low emissivity glass construction.
U.S. Pat. No. 4,900,634 assigned to Glaverbel discloses a pyrolytic coating of tin oxide containing a mixture of fluorine and antimony dopants coated on glass and imparting low emissivity and a specific haze reduction factor of at most 1.5.
U.S. Pat. No. 5,168,003, assigned to Ford Motor Company, describes a glazing article bearing a substantially transparent coating comprising an optically functional layer (which may be low emissivity or solar control) and a thinner anti-iridescence layer which is a multiple gradient step zone layer. Antimony doped tin oxide is mentioned as a possible alternative or optional component of the exemplified low emissivity layer.
U.S. Pat. No. 5,780,149, assigned to Libbey-Owens-Ford describes solar control coated glass wherein at least three coating layers are present, first and second transparent coatings and an iridescence suppressing layer lying between the glass substrate and the transparent upper layers. The invention relies upon the transparent layers having a difference in refractive indices in the near infrared region greater than the difference of indices in the visible region. This difference causes solar heat to be reflected in the near IR region as opposed to being absorbed. Doped metal oxides which have low emissivity properties, such as fluorine doped tin oxide, are used as the first transparent layer. Metal oxides such as undoped tin oxide are used as the second layer. No NIR absorbing combinations are described.
EP 0-546-302-B1 issued Jul. 16, 1997 and is assigned to Asahi Glass Co. This patent describes coating systems for solar-control, heat treated (tempered or bent) glass comprising a protection layer based on a metal nitride. The protection layer or layers are used to overcoat the solar-control layer (to prevent it from oxidizing during thermal treatment). As a solar control layer, many examples are provided including tin oxide doped with antimony or fluorine. However, the specific combination of doped SnO2 layers of the present invention that accomplishes solar control, low emissivity and anti-iridescence without following Gordon""s teachings is neither disclosed nor exemplified.
EP 0-735-009-A1 is a patent application that was published in February 1996 and is assigned to Central Glass Co. This patent application describes a heat-reflecting glass pane having a multilayer coating comprising a glass plate and two layers. The first layer is a high refractive index metal oxide based on Cr, Mn, Fe, Co, Ni or Cu, the second layer is a lower refractive index film based on a metal oxide such as tin oxide. Doped layers and low emissivity or NIR absorbing combinations are not disclosed.
WO 98/11031 This patent application was published in March 1998 and assigned to Pilkington PLC. It describes a high performance solar-control glass comprising a glass substrate with coatings comprising a heat-absorbing layer and a low emissivity layer of a metal oxide. The heat-absorbing layer may be a metal oxide layer. This layer may be doped tungsten, cobalt, chromium, iron molybdenum, niobium or vanadium oxide or mixtures thereof. The low emissivity layer may be doped tin oxide. In a preferred aspect of the invention, an iridescence-suppressing layer or layers is incorporated under the coating comprising a heat-absorbing layer and a low emissivity layer. This application does not disclose or suggest the specific combination of doped SnO2 layers of the present invention that accomplishes solar control, low emissivity and anti-iridescence without requiring a xe2x80x9cGordonxe2x80x9d type underlayer to suppress iridescence or color reflection.
Canadian Patent 2,193,158 discloses an antimony doped tin oxide layer on glass with a tin to antimony molar ratio o 1:0.2 to 1:0.5 that reduces the light transmission of the glass.
Dopant Effects in Sprayed Tin Oxide Films, by E. Shanthi, A. Banerjee and K. L. Chopra, Thin Solid Films, Vol 88, 1981 pages 93 to 100 discusses the effects of antimony, fluorine, and antimony-fluorine dopants on the electrical properties of tin oxide films. The article does not disclose any optical properties of the antimony-fluorine films nor the effect on transmitted or reflected color.
UK Patent Application GB 2,302,101 A assigned to Glaverbel describes a glass article coated with an antimony/tin oxide film of at least 400 nm containing an Sb/Sn molar ratio from 0.05 to 0.5, with a visible transmittance of less than 35%. The films are applied by aqueous spray CVD and are intended for privacy glass applications. Haze reducing undercoats are taught as well as thick layers with low Sb/Sn ratios which have low emissivity properties as well as high solar absorbency. It also teaches that it is possible to provide one or more additional coating layers to achieve certain desirable optical properties. None of these properties other than haze are mentioned. The application teaches nothing about thinner layers, the use of more than one dopant, or the control of film color.
UK Patent Application GB 2,302,102 A also assigned to Glaverbel describes a glass substrate coated with a Sn/Sb oxide layer containing tin and antimony in a molar ratio of from 0.01 to 0.5, said layer having been deposited by CVD, whereby the coated substrate has a solar factor(solar heat gain coefficient) of less than 0.7. The coatings are intended for window applications and have luminous transmittances between 40 and 65% and thicknesses ranging from 100 to 500 nm. Haze reducing undercoats are claimed and low emissivity can be imparted to the coatings by a judicious choice of the Sb/Sn ratio. Like the previous application, the teaching of providing one or more additional coating layers to achieve certain desirable optical properties is mentioned. Also low emissivity layers of fluorine doped tin oxide can be deposited over the Sb/Sn layers or fluorine components can be added to the Sb/Sn reactants to give low emissivity films which contain F, Sb and Sn. The last two methods were not favored because of the added time and cost of adding a third layer and the fact that the emissivity of the Sb/F films was raised and not lowered. No mention of color control or color neutrality is found.
GB 2,200139, assigned to Glaverbel teaches a method of depositing a coating by the spray application of solutions containing tin precursors, fluorine containing compounds and it least one other dopant selected from the group antimony, arsenic, vanadium, cobalt, zinc, cadmium, tungsten, tellurium or manganese.
Previously, glass manufacturers have managed heat transport through windows by the use of absorbing and/or reflecting coatings, glass tints, and post-applied films. Most of these coatings and films are designed to control only one portion of the solar heat spectrum, either the NIR, i.e. near infrared component of the electromagnetic spectrum having a wavelength in the range of 750-2500 nm or the mid IR component of the electromagnetic spectrum having a wavelength on the range of 2.5-25 microns. A product has been designed to control the entire heat spectrum, however Sputtered metal/dielectric film stacks while effective, have limited durability and must be protected and sealed within the center section of a multipane insulated glass unit (IGU). What is needed is a total solar control film or combination of films that can be easily applied by pyrolytic deposition during the glass making operation which yields an article which has an acceptable visible transmission, reflects or absorbs the NIR, reflects the mid-IR, and is neutral or close to neutral in color.
The above references either alone or in combination do not teach or suggest the specific combination of doped SnO2 layers of the present invention that accomplishes solar control, low emissivity and anti-iridescence without requiring a xe2x80x9cGordonxe2x80x9d type underlayer.
The present invention provides an improved solar-control glass that has acceptable visible light transmission, absorbs near infrared wavelength light (NIR) and reflects midrange infrared light (low emissivity or Low E) along with a preselected color within the visible spectrum for reflected light that can be controlled to a specific color or be made essentially colorless (xe2x80x9cneutralxe2x80x9d as defined hereinafter). Also provided is a method of producing the improved, coated, solar-control glass. The improved glass coating is a tin oxide coating with various dopants and haze modifiers in specific layers of the coating. One layer is a solar energy (NIR) absorbing layer comprising tin oxide having a dopant such as antimony. Another layer in the tin oxide coating is a low emissivity control layer capable of reflecting midrange infrared light and comprising tin oxide having fluorine and/or phosphorus dopant. A separate iridescence color suppressing layer as described in the prior art such as a xe2x80x9cGordonxe2x80x9d layer is generally not needed to achieve a neutral (colorless) appearance for light reflected off the coated glass, however an iridescence suppressing layer or other layers may be combined with the multilayer tin oxide coating provided by the present invention. If desired, multiple solar control and/or multiple low emissivity layers can be utilized. The NIR layer and the low emissivity layer are separate portions of a single tin oxide film since both layers are composed of doped tin oxide. A method of producing the coated solar control glass is also provided. In addition, the present invention controls or changes the color of transmitted light through the addition of color additives to the NIR layer. Surprisingly the dopant fluorine that produces a noncolored tin oxide film functions as a color additive when added as an additional dopant to the NIR layer and modifies the color of transmitted light through the NIR film. Also provided are haze reducing dopants in specific layers of the tin oxide coating.